1. Field of the Invention
This invention relates generally to an ignition system for an internal combustion engine, and more specifically, to a direct ignition system for an internal combustion engine incorporating magnetic sensors for sensing cam and crank shaft positions.
2. Background and Summary of the Invention
In an internal combustion engine, it is a requirement that means be included to synchronize both the injection of fuel, ignition firing and exhaustion of each of the cylinders of the engine. Conventional internal combustion engines generally utilize a distributor to perform this operation. Many modern internal combustion engines, however, incorporate distributorless ignition systems sometimes referred to as direct ignition systems (DIS). In a DIS, magnetic sensors are generally incorporated to detect the engine position, i.e., the piston stroke and speed for each cylinder, by sensing the rotation of the crank and cam shafts, and thus, to determine which cylinders are to receive fuel, ignition firing, etc. These sensors combined with an onboard computer provide an intricate and reliable method for determining engine position and have greatly improved control of fuel injection and ignition firing over the conventional distributor. Other advantages of distributorless ignition systems include reduction of spark scatter caused by certain mechanical components of the ignition system.
It is known in the art to include a magnetic position sensor in conjunction with the engine's flywheel to sense crank shaft position. It is further known to include a magnetic position sensor in conjunction with the cam sprocket of the cam shaft to sense cam shaft position. The signals associated with the crank and cam shaft positions can then be deciphered to determine the appropriate sequence of fuel injection, ignition firing and exhaustion to each of the cylinders. Typically, in these prior art systems the flywheel will include a specially configured array of markings whose positions can be detected by the magnetic sensor. Further, the cam sprocket will also include a predetermined configuration of markings also detectable by the other magnetic sensor. Consequently, the flywheel and cam sprocket require additional customized components over the conventional flywheel and cam sprocket to accommodate the markings.
Because of the nature of the detection of the markings on these components, certain rigorous tooling procedures are required providing intense accuracy and precision. The complexity of these components demands extensive lead time and further reduces flexibility. Other precision requirements include tight tolerances of the air gap between the magnetic sensors and the customized components. For example, since the magnetic sensor associated with the crank shaft is generally positioned within a housing and is connected to the transmission, the magnetic sensor is mounted to the housing by means of a movable support such that the position between the magnetic sensor and the crank shaft is adjustable. Although these prior art systems have operated successfully, the rigid tolerances and added components of the prior art systems add an undesirable cost and weight to the finished product.
Once the system described above is accurately assembled and in operation, it still suffers from a number of undesirable characteristics. Specifically, the system requires the crank and cam shafts go through a minimum rotational speed to provide a proper signal to the onboard computer before the computer authorizes a "first fire" of the first cylinder. Because of this, the computer must wait for some period after the engine operator first initiates start-up of the engine before the computer can synchronize the proper sequence of fuel injection and ignition firing. This provides a certain drain on the battery which may ultimately effect engine start-up during such times as in cold weather.
What is needed then is a direct ignition system incorporating sensing of the cam shaft and crank shaft position, but which does not include added high precision components, and further, which does not incorporate a delay of the "first fire" of the first cylinder during engine start-up. It is therefore an object of the present invention to provide such a method and apparatus.
Disclosed is a direct ignition system for use with an internal combustion engine. In one preferred embodiment, a magnetic sensor, typically a solid state hall effect switch, is positioned relative to a specific counter weight integral with the crank shaft. The counter weight is comprised of a magnetic material having specific patterns of grooves or slots spaced apart from each other in a predetermined arrangement. One of the grooves is a signature groove which is generally of a substantially wider dimension than the remaining grooves. The patterns of grooves are separated into specific sets representing the stroke position and speed of a particular set of pistons operating in unison. As the counter weight including the detection grooves rotates relative to the hall switch, the magnetic field of a magnet within the hall switch will be decreased as each groove passes in front of the sensor. The last groove of a groove set indicates at what point the set of pistons representative of that group is at top dead center, i.e., when the pistons are completely inserted within their respective cylinders.
The cam shaft also includes a magnetic sensor, also typically a solid state hall effect switch. In contrast to the magnetic sensor associated with the crank shaft, the magnet of the cam shaft magnetic sensor is generally not included within the hall switch, but is positioned at an end of the cam shaft opposite the cam sprocket. The magnet typically includes an array of alternating north and south poles. In general, the poles of the magnet are arranged in a specific keyed pattern relative to the lobes controlling the valve positions such that sections of specific poles are of different areas relative to other sections of poles. The hall switch itself is rigidly connected to the cylinder head of the engine block. Since the magnetic sensor is attached adjacent to the end of the cam shaft, it can also act as a thrust plate to control cam shaft play within the cylinder head. By this configuration, the hall switch can determine whether a particular cylinder is in a compression or exhaust stroke.
As is well known, the cam shaft turns at one revolution per every two revolutions of the crank shaft. As the cam shaft rotates the hall switch produces an output pattern in which the signal goes from low to high or high to low during a transition between two adjacent poles. In addition, the output of the hall switch adjacent the crank shaft counter weight goes from low to high and high to low as each groove passes by the sensor while the crank shaft is rotating. Since the output pattern of the hall switch adjacent the crank shaft gives output information concerning which set of pistons is at what location, as well as the speed at which they are moving, and the cam shaft hall switch gives compression and exhaust information of specific cylinders, the onboard computer can determine which cylinder of the set of cylinders would be in an exhaustion sequence and which one is in a compression sequence requiring fuel injection for firing. Only once during a cam shaft revolution would the transition go from "high" to "low" during detection of the crank shaft signature slot. Any other transition from "high" to "low" occurs when the crank signal is low. Therefore, the onboard computer can determine within one revolution of the crank shaft which cylinder requires firing.